Electric train services between between Edinburgh and Glasgow is unlikely to be completed by December this year - seven months behind schedule.

Transport Minister Humza Yousaf admits he is "concerned and disappointed" by the analysis of Network Rail's performance, which also showed "slow progress" on improvement work to the Highland mainline and the Aberdeen to Inverness route.

He has ordered Transport Scotland officials to carry out a review of the governance of major rail projects.

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In its annual assessment of Network Rail, the Office of Rail and Road (ORR) said it has concerns "regarding the ability of key projects to meet their obligations and regulatory milestones".

Its report identified "systemic issues around project planning and delivery" and said "affordability and deliverability risks" are emerging for projects in the earlier stages of development and delivery.

The ORR said "increasing cost estimates" are beginning to put pressure on Network Rail's funding cap for the period April 2014 to March 2019.

The report also praised progress made on health and safety and Network Rail's programme to improve asset reliability.

Tunnel works continue at Queen Street Station (Image: SNS Group)

Chief executive Joanna Whittington said: "Network Rail has successfully delivered some major enhancement projects in the past year, including Scotland's first new rail line in over 100 years, the Borders Railway.

"However, there are cost and delivery issues on other projects which need to be addressed.

"Over the course of the next year, we need to see evidence that Network Rail's initiatives are delivering financial efficiencies and noticeable performance improvements for passengers while achieving gains in health and safety."

Mr Yousaf added: "Network Rail has informed Transport Scotland that the Edinburgh-Glasgow line will not be running electric services until July 2017.

"This is seven months later than scheduled and seven months later than they advised ministers two months ago. This will also increase the cost of the project beyond the previous £742million estimate.

"Network Rail's cost estimates for a number of other major projects which are at earlier stages of delivery have also increased. Moreover, progress on other projects has also been slower than expected.

"I am not prepared to simply accept the long-term cost implications, nor the revised programmes that Network Rail have set out. I will also be doing everything possible to ensure that Network Rail deliver the full programme in Scotland by March 2019 and without any extra funding from the Scottish Government."

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Mr Yousaf said he expects the Transport Scotland review to be completed by September, after which he expects senior Network Rail officials to come before Holyrood's Rural Economy and Connectivity Committee to answer questions.

Phil Verster, managing director of Network Rail Scotland and of the ScotRail Alliance said: "Our Network Rail project teams and their suppliers have a strong and proud track record in Scotland of delivering on-time and on-budget. We need look no further than the Borders Railway line to see evidence of that.

"The programme impacts highlighted today will not delay the introduction of our exciting new fleet of faster, longer, greener trains - nor will they impact on our ability to deliver the 200 new services and 20,000 extra seats promised in the Revolution in Rail timetable change.

"Very importantly, our teams have learnt valuable lessons from the circumstances, decisions and programme impacts over the last months.

"The Edinburgh-Glasgow Improvement Programme is still progressing well and, as the ORR indicated today, the costs have risen due to extra compliance requirements, complicated interfaces with other projects and other unforeseen factors such as severe weather impacts.

"Despite this, I am pleased to confirm that we are committed to still deliver the overall railway enhancement programme for Scotland by March 2019, and within the agreed funding limits."